Fractional flow reserve (FFR) and index of microcirculatory resistance (IMR) relationship in patients with chronic or stabilized acute coronary syndromes.

AIMS

To investigate the influence of index of microcirculatory resistance (IMR) on fractional flow reserve (FFR) and adenosine-induced hyperemia (ΔPd/Pa-FFR) in patients with chronic (CCS) or stabilized acute coronary syndromes (ACS), utilizing various IMR threshold values.

METHODS

Data were extracted from two ongoing Italian registries involving patients with CCS or stabilized ACS who underwent a #FullPhysiology approach [Pd/Pa, FFR, IMR, coronary flow reserve (CFR)] by bolus thermodilution technique in the left anterior descending artery. Correlations between IMR and both FFR and ΔPd/Pa-FFR were analyzed both globally and within three IMR-defined groups: Group 1 (IMR <25), Group 2 (25 ≤ IMR <40), and Group 3 (IMR ≥40). A multiple linear regression was employed to adjust for confounding factors.

RESULTS

Of 275 patients, 163 were in Group 1, 60 in Group 2, and 52 in Group 3. Globally, a weak but significant correlation was observed between IMR and both FFR (r = 0.170, p < 0.01) and ΔPd/Pa-FFR (r = -0.159, p < 0.01). After stratification only patients in Group 3 exhibited a significant and more pronounced, though still weak, correlation between FFR and IMR (r = 0.387, p < 0.01) coupled with a reduction of ΔPd/Pa-FFR as IMR values increased (r = -0.411, p < 0.01). After adjustment, a significant increase of 0.01 in FFR values was observed for every 14-unit rise in IMR (p < 0.01) in Group 3.

CONCLUSIONS

FFR appears particularly influenced by elevated IMR values (≥40) highlighting the importance of the #FullPhysiology approach in understanding epicardial and microvascular contribution of myocardial ischemia.